The present invention relates to the field of communication networks, and more specifically to voice transport networks having one or more circuit-switching sub-networks and one or more packet transmission sub-networks, with gateway interfaces to interconnect them.
The development of the Internet network has greatly contributed to the appearance then expansion of telecommunication services designed to operate in accordance with the protocol suite of this network, in particular the IP (Internet Protocol, Request for Comments (RFC) 760, Internet Engineering Task Force (IETF), January 1980) network layer protocol.
Telephony services, developed first around circuit-switching techniques, then more recently proposed on IP networks, are one example of this transformation. High-performance integrated networks are being designed today, offering voice and data transport services and operating entirely using the IP protocol.
However, the underlying economic and technical requirements impose that a seamless transition takes place, meaning that a technology jump cannot reasonably be considered. It is appropriate to contemplate an intermediate step during which heterogeneous networks, arising from the interconnection of traditional PABX (Private Automatic Branch eXchange) networks with networks operating entirely using the IP protocol, will be developed.
Such heterogeneous networks may for example include one or more Local Area Networks (LANs) operating using the IP protocol, interconnected with one or more traditional PABX networks forming a “multi-site” network.
A PABX network generally incorporates a set of telephony applications including a communication path supervision application. For each communication admitted by the topology of the network, such an application determines, according to the network's topological description data to which it has access and according to input parameters specific to the communication, a communication path which may then be reserved and then used.
The determination of such a path, more specifically the choice of topological nodes that come one after the other along the path, takes place preferably independently of the technology used to form each of the routes linking these nodes. In the OSI reference model, the process does not fall beneath the network layer. For example, the communication path supervision application is not concerned as to whether the path between two nodes makes use of a 64 kbit/s PCM link or an IP-based LAN. Next a link-layer process takes charge of implementing the switching path, that is reserving appropriate resources along the determined path and managing the use of these resources.
During configuration of the PABX network, network management software is used to declare the routes capable of transporting the determined type of traffic. The parameters of this declaration include in particular the route type, the corresponding topological nodes, the voice traffic transport parameters (in particular the coding laws), etc. The PABX network topology is therefore known by at least some of the network applications, in particular the communication path supervision and setup applications.
This intelligence is absent from networks operating using the IP protocol since, in such a network, the routing of datagrams, whether or not they transport voice, is performed by mechanisms internal to the network which do not interact with the client applications to determine the path used by each packet. Only the IP address of the recipient is taken into account. The RSVP (“Resource ReSerVation Protocol”, RFC 2205, IETF, September 1997) protocol intended to increase the quality of service offered to users of IP networks does not bring about any change since it relies on the IP routing mechanisms, and remains an IP network tool, unlike in the case of PABX networks which specifically incorporate path supervision and setup tools.
The success of IP networks has led to the development of applications for the transport of voice over IP networks, raising the possibility of traditional PABX networks eventually being replaced by multi-service IP networks. Most developers are studying systems operating entirely using the IP protocol. Solutions intended for heterogeneous networks, made up partly of one or more IP protocol transmission networks and partly of one or more PABX networks, are not being studied much.
An object of the present invention is to improve interaction between the various types of networks forming a heterogeneous communication system, in order to optimize use of all the resources of the network.